The transdermal route of parenteral delivery of drugs provides many advantages over other administrative routes, and transdermal systems for delivering a wide variety of drugs or other beneficial agents are described in U.S. Pat. Nos. 3,598,122, 3,598,123, 4,379,454, 4,286,592, 4,314,557 and 4,568,343, for example, all of which are incorporated herein by reference. In many instances, drugs which would appear to be ideal candidates for transdermal delivery are found to have such low permeability through intact skin that they cannot be delivered at therapeutically effective rates from reasonably sized systems.
In an effort to increase skin permeability, it has been proposed to pretreat the skin with various chemicals or to concurrently deliver the drug in the presence of a permeation enhancer. Various materials have been suggested for this purpose, as described in U.S. Pat. Nos. 3,472,931, 3,527,864, 3,896,238, 3,903,256, 3,952,099, 4,046,886, 4,130,643, 4,130,667, 4,299,826, 4,335,115, 4,343,798, 4,379,454, 4,405,616 and 4,746,515, all of which are incorporated herein by reference; British Pat. No. 1,001,949; and Idson, Percutaneous Absorption, J. Pharm. Sci., vol. 64, No. b6, June 1975, pp 901-924 (particularly 919-921).
To be considered useful, a permeation enhancer should have the ability to enhance the permeability of the skin for at least one and preferably a significant number of drugs. More importantly, it should be able to enhance the skin permeability such that the drug delivery rate from a reasonably sized system (preferably 5-50 cm.sup.2) is at therapeutic levels. Additionally, the enhancer, when applied to the skin surface, should be non-toxic, non-irritating on prolonged exposure and under occlusion, and non-sensitizing on repeated exposure. Preferably, it should be odorless and capable of delivering drugs without producing burning or tingling sensations.
The present invention greatly increases drug permeability through the skin, and also reduces the lag time between application of the drug to the skin and attainment of the desired therapeutic effect.
While it is known in the art to combine permeation enhancers, this invention utilizes a novel combination of ethanol and a mixture of monoglycerides with a total monoesters content of at least 90%. The combined effect produces a significant and surprising improvement over use of not only either monoglyceride or ethanol alone but also over the combination of ethanol and a monoglyceride such as glycerol monooleate (GMO) of lesser purity and lower monoesters content.